1. Technical Field
The present invention relates to the field of speech recognition and, more particularly, to the generation of a grammar for use with a speech recognition system.
2. Description of the Related Art
Conventional data processing systems frequently incorporate speech-based user interfaces to provide users with speech access to a corpus of data stored and managed by a data processing system. To adequately process user requests or queries, however, a speech recognition system must have the ability to recognize particular words which are specified within the corpus of data, and therefore, words which likely will be received as part of a user request. Thus, the speech recognition system must include a speech recognition grammar which lists relevant, if not all, terms included within the corpus of data.
From a speech recognition perspective, simply including all possible words of a corpus of data within a speech recognition grammar can lead to an extremely large and inefficient grammar. An oversized speech recognition grammar can lead to ambiguities when converting speech to text, and therefore, decreased speech recognition accuracy. An oversized grammar further can result in increased search times when recognizing user spoken utterances. In consequence, efforts have been made to reduce the size of speech recognition grammars while still ensuring that relevant and adequate vocabulary is specified for searching a large corpus of data.
One solution used to generate speech recognition grammars from a corpus of data has been to identify keywords from the corpus of data and include those keywords within the speech recognition grammar. Because only those words considered to be keywords are included within the grammar, the size of the grammar can be limited, at least when compared to the size of the entire corpus of data. The keywords typically are derived or identified from an empirical analysis of the corpus of data to identify important words or from a statistical analysis of the corpus of data to identify words having a minimum frequency of appearance. The keyword method seeks to ensure that the most relevant or important terms of a corpus of data are included within the grammar.
Using keyword or other related word spotting techniques for generating speech recognition grammars does have disadvantages. One such disadvantage is that the speech recognition grammars generated using keyword techniques are domain specific. Accordingly, for each identifiable domain of a data corpus, or for each distinct corpus of data, keywords first must be identified as previously discussed. Keyword identification in and of itself can be both time and resource intensive and must be entirely duplicated for each different domain being processed. That is, the generation of a speech recognition grammar for one particular domain provides no benefit or advantage when developing a speech recognition grammar for a different domain. The process, including keyword identification, must be started anew for each domain.
Another disadvantage of using keyword techniques for generating speech recognition grammars is that the grammars must be updated continually as the corpus of data changes and as the underlying subject matter evolves. As new sources of information are added to a corpus of data, so too must new keywords be identified from the sources so that important terminology can be included within the speech recognition grammar. In consequence, the maintenance of keyword style grammar can be costly and time consuming. The disadvantages of maintaining such a grammar are exacerbated in the case where a set of domain specific speech recognition grammars are to be maintained as each grammar must be maintained independently of the others.